Currently, comprehensive and low-cost test methodologies for analog and mixed-signal systems analogous do not exist. Test methodologies for mixed-signal systems are based primarily on the paradigm of measuring the circuit's specifications to determine if they are “good” or “bad”. This method is known as specification based testing. With this method of testing, each specification is measured for each circuit, e.g., an integrated circuit (IC), to ensure that the circuit satisfies all specified parameters.
Specification based testing has many drawbacks. Foremost perhaps is the cost associated with such testing. Testing costs include both the cost of test development as well as the costs associated with conducting the actual manufacturing tests. The cost factor becomes critical in high volume production of analog and mixed-signal ICs. Most of the previous research in test generation for fault detection in analog circuits assumes that a list of faults for which tests are to be generated is given. This approach is known as fault based testing. Realistic fault lists can be generated from analysis of the circuit layout using inductive fault analysis (IFA) based techniques.
In the past, test researchers have proposed eliminating some of the tests from the conventional specification test set to reduce production test cost. Theses researchers have been motivated by the fact that many of the specification tests contain redundant information about the underlying process defects. For instance, the correlation between specification tests has been used for test elimination. A more rigorous approach for test elimination based on QR factorization of linear models has also been proposed. During production testing, not only the number of tests but also the order in which they are performed affect the overall testing time and test quality. Thus, a further reduction in average production testing time can be achieved by performing those specification tests first, which take the least time and have the maximum fault coverage. A graphical theoretic approach has also been used to optimize specification tests. Although the tests derived using the above mentioned testing schemes can substitute for the conventional specification tests performed during the final test stage of analog circuits, these test methodologies again resort to costly (although optimized) specification tests for fault detection.
From the foregoing, it can be appreciated that it would be desirable to have a testing method for circuits, such as analog ICs, which accurately predicts circuit performance and which is low in cost to develop and perform.